Quantum cascade lasers generate light in the mid- to far infrared (IR) using inter-subband transitions in a repeated stack of semiconductor multiple quantum well heterostructures. A spectroscopy system based on these tunable lasers and various applications for such a system have been discussed by Kotidis et al., in U.S. Pat. No. 8,780,347 B2, entitled “QCL Spectroscopy System and Applications Therefor”, which is herein incorporated by reference in its entirety.